Chinook salmon spawning at Vernita Bar
You may notice the level of the Columbia River has dropped this month.
It’s the annual flow adjustment to aid chinook salmon laying their eggs on the Vernita Bar, a large gravel bar in the river four miles downstream from Priest Rapids Dam.
There and in three other places in the Hanford Reach of the Columbia River just above Richland, salmon dig nests, called redds, in the gravel to lay their eggs.
Each year as the chinook salmon return like clockwork to spawn, river levels below the Priest Rapids Dam are reduced in mid October during the day, says the Bonneville Power Administration.
Chinook spawn mostly during the day.
The lower river level encourages them to dig redds lower on the riverbanks to make sure that as water levels drop, the nests do not end up on dry land.
The nests need to remain underwater until the fish emerge in the spring.
The salmon use their powerful tails to clear aside the rocks in nests about 20 feet apart.
After the eggs are laid, the salmon move the rocks back, sweeping rocks into place that may be as large as eight inches across. Each redd may have as many as 4,500 eggs.
At night, flows are increased to release any excess water to downriver.
Historically, scientists believed a relatively small number of chinook spawned in the Vernita Bar area.
But river operations during some seasons have helped to increase that number to as many as 250,000 salmon, according to BPA.
Salmon spawns are nurtured by keeping river levels low when salmon spawn, but higher during the winter and spring to keep as many eggs and emerging fry under water as possible.
It’s most profitable for water to be released from the dams during the day, making power when people are using it. But that’s not what’s best for salmon in the fall.
Water levels also are adjusted in the Columbia River below Bonneville Dam for spawning chum salmon in November.
Called “dog” salmon because of their canine-like teeth, chum are the last salmon of the year to return to the Columbia to spawn, and their young are the first to leave for the ocean in the spring.
Chum salmon generally spawn in the lower part of the Columbia River below Bonneville Dam, in areas where warm water pushes up through the ground into the gravel where salmon make their nests.
BPA says the hatchery programs it has paid for and the construction of new spawning areas have allowed as many as 20,000 chum a year to return to the Columbia River.
The federal government listed Columbia River chum as threatened under the Endangered Species Act in 1999.